Various characteristics that the edge controls the vibration of the diaphragm, the edge itself does not cause an abnormal vibration such as a resonance, etc., and also the edge has an internal loss necessary for decaying an excess vibration of the diaphragm have been required for an edge formed at the peripheral portion of the diaphragm of a loudspeaker to improve the sound characteristics.
Hitherto, for satisfying the requirements, various kinds of edges comprising, for example, the following materials have been developed.
That is, (1) a fiber type edge prepared by impregnating a woven fabric or a nonwoven fabric of natural fibers or synthetic fibers with a thermosetting resin, shaping the fabric by heat-pressing, and finishing by coating it with a damping agent (decaying agent), (2) an urethane compressed type edge prepared by impregnating an urethane foam expanded to about 30 times with a bitumen and shaping the foam by heat-pressing followed by finishing, and (3) a rubber type edge prepared by using a rubber mixture containing a vulcanizing agent and molding it using a predetermined mold followed by finishing.
However, the above-described various kinds of edges each has the following defects.
That is, in the edge of the type (1), the coating work of the damping agent is complicated and the products obtained have a scatter in quality. In the urethane compressed type edge (2), the bitumen oozes out. Further, since the hardness of the molded products is changed by an environmental temperature, a scatter in the tone quality sometimes occurs in the loudspeakers using the products as the edges. Also, the edge has the problem that it is poor in a weather resistance and a water resistance. The rubber type edge (3) described above increases weight of the product itself due to the molded material. Accordingly, the edge cannot follow the vibration of the diaphragm, which results in lowering the sensitivity of the loudspeaker.
As described above, conventional various edges each has the respective problem and hence a loudspeaker member having a high quality, having a good workability, being less influenced by an environmental temperature, and having excellent sound characteristics has been desired.